Conventionally, a discharge muffler has been known, which cancels noise of refrigerant gas discharged from a compressor and containing refrigerating machine oil. As described in Patent Document 1, as the discharge muffler of this type, there is a discharge muffler including an oil return pipe for discharging refrigerating machine oil accumulated in the discharge muffler.
The discharge muffler is provided on an outlet side of a high-pressure compression mechanism in an intermediate-pressure dome type two-stage compressor (i.e., a two-stage compressor in which an inside of a casing of the compressor is under a discharge pressure of a low-pressure compression mechanism). The discharge muffler includes an elongated cylindrical volume portion (muffler container) which is closed at upper and lower ends, and a supply pipe (inlet path), a discharge pipe (outlet path), and the oil return pipe are connected to the volume portion.
An inlet end of the supply pipe is connected to the outlet side of the high-pressure compression mechanism, and an outlet end of the supply pipe is positioned in an upper space inside the volume portion with the supply pipe penetrating an upper surface of the volume portion. An inlet end of the discharge pipe is positioned in a lower space inside the volume portion, and an outlet end of the discharge pipe is positioned outside the volume portion with the discharge pipe penetrating the upper surface of the volume portion. An inlet end of the oil return pipe is connected to an opening provided in a bottom surface of the volume portion, and an outlet end of the oil return pipe is connected to an opening provided in the casing of the two-stage compressor.
In the discharge muffler, refrigerant gas discharged from the high-pressure compression mechanism and containing refrigerating machine oil flows into the upper space inside the volume portion through the supply pipe. The refrigerant gas flowing into the upper space flows toward the lower space inside the volume portion while turning along an inner circumferential surface of the volume portion. While the refrigerant gas flows toward the lower space, noise of the refrigerant gas is canceled, and the refrigerating machine oil contained in the refrigerant gas is separated from the refrigerant gas by centrifugal force caused due to the turning of the refrigerant gas. Then, the refrigerant gas from which the refrigerating machine oil is separated flows out from the volume portion through the discharge pipe. The refrigerating machine oil separated from the refrigerant gas is temporarily stored in the lower space, and then is discharged to the casing of the two-stage compressor through the oil return pipe.